A new type of permeable, reactive composite is being developed for remediation and management of contaminated sediments. It consists of one or more filtering layers surrounding a reactive layer placed on the sediment surface. Hydrodynamic dispersion and pore fluid flow carry contaminants through the composite. The broad, long-term objective of this research is to develop a comprehensive understanding of: 1) how the gecicomposite would function most effectively in long-term field applications for different combinations of sediment types, sediment contaminants and pore fluid environments;and 2) how effectively the composite can reduce ecological and human health risks associated with sediment-bound contaminants. The specific aims of the research are to address the following fundamental issues: 1) What are the reactive materials that can be used in the composite that will most effectively immobilize or transform the target contaminants of PCB's, polyaromatic hydrocarbons (PAHs), and metals? 2) What is the relationship between the advective and diffusive components of contaminant transport for various soil-contaminant-pore fluid chemistry combinations? 3) How can results from bench-scale experiments that model the sediment-contaminant- composite system be used to predict the composite's scalability for field applications? 4) What are the effects of the physical presence of the composite and the composite-contaminant reactions on both the underlying sediment and overlying benthic organisms, in terms of supporting healthy and diverse benthic communities in these zones? 5) Does the geocomposite reduce the human health risks associated with contaminated sediments? The research will be performed in 4 phases: 1) sediment characterization for each Superfund site sediment to be tested, including physical, chemical, biological and consolidation testing;2) batch chemical testing to assess and optimize reactivity between target contaminants and the composite reactive amendments to be testing in Phase 3;3) bench scale tests to model the sediment-composite-benthic system using a computer automated device that combines sediment consolidation and contaminant transport through the sediment and composite, and assess the biological activity before and after sediment consolidation, as well as the biogeneration in the overlying 'clean'sediment;and 4) modeling of the process, accounting for seepage, consolidation, dispersion and reactivity due to adsorption and transformation. Relevance to Public Health: Contaminated sediments present a global public health challenge that requires new, innovative approaches. By immobilizing and/or neutralizing contaminants, the composite has the potential to minimize further contaminant migration and, in subaqueous environments, contaminant resuspension and diffusion into the overlying water column. This will limit the bioavailability of contaminants and bioaccumulation in aquatic food webs, which can be a pathway for human exposure via ingestion.